A derogatory term used to describe particuly fat women, who are annoyed by their unsightly appearance and take it out on everyone by being arrogent, obnoxious and annoying. Unfortunately this bitchy behaviour leads to even more females excluding them and more males vowing to never tap that shiz. This causes the syptoms of FBS to worsen and continue the vicious cycle, until the female in question does what everyone has hoped for and goes and dies in fire, thereby annoying everyone no more.

Beth/Ashlyn: "ZOMFG I know everything, I am better than you all, I hate you all and I'm sure as not easy on the eyes"
Chops: "LoL guyz, I say there's a severe case of FBS (fat bitch syndrome)"
p0undy and richo: "here here"

When a heavier woman acts in ways that aren't normal or positive to garner any attention she can from others.

"Last night Bertha was starting so much drama because she wanted Rick to notice her and she wanted to keep his attention off of the better looking girls. That hooker has serious F.B.S. (Fat Bitch Syndrome)."